|Publication number||US7911352 B2|
|Application number||US 12/273,226|
|Publication date||Mar 22, 2011|
|Priority date||Nov 19, 2007|
|Also published as||US20090128347, WO2009067467A2, WO2009067467A3|
|Publication number||12273226, 273226, US 7911352 B2, US 7911352B2, US-B2-7911352, US7911352 B2, US7911352B2|
|Inventors||Thomas John Bucella, Thomas P. Dombroski, David E. Fuchs, Jeremy M. Block|
|Original Assignee||Teknic, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (13), Non-Patent Citations (2), Referenced by (3), Classifications (17), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims one or more inventions which were disclosed in Provisional Application No. 60/988,947, filed Nov. 19, 2007, entitled “Method and Apparatus for Protection of AC-DC power Converters”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.
1. Field of the Invention
The invention pertains to the field of AC-DC power converters. More particularly, the invention pertains to protection of such converters.
2. Description of Related Art
Electrical and electromechanical machines often include AC-DC power converters that convert incoming AC power to another type of power for use by devices (loads). Examples of power conversion include AC to DC rectifiers, voltage step-down converters, voltage step-up converters. Often, the AC power supplied to and/or the DC power produced by the AC-DC Power Converter is considered hazardous to humans and/or supplies loads that are hazardous to humans (Hazardous).
There is a need to protect the AC-DC Power Converters and their loads from connection to the wrong type of power, incorrect power connections, poor power quality, wiring shorts and overloads. When the power or load is Hazardous, there is also a need to insure that the power to the power converter is securely disconnected when a safety event (e.g., emergency stop) or a safety lockout occurs.
Today, upstream protection devices used to protect AC-DC power converters e.g., circuit breakers, fuses, etc. operate independently from the AC-DC power converter. As such, these upstream devices are generally limited in their functionality because they are unaware of the effect of the incoming power on the AC-DC power converter and their loads. In addition, when the power is Hazardous, a safety-switching device and controller are often used to ensure safety in a machine by securely disconnecting power to the AC-DC power converter. In both of these examples more protection, seamless power sequencing and other added functions can be accomplished if the AC-DC power converter is responsible for controlling an upstream switching device for these protection functions.
An AC-DC power converter controls an external upstream switching device, which supplies it power to be converted. Power conversion is initiated when an external signal requests power be converted or when a program within the AC-DC power converter detects the need for power conversion. When this occurs, the AC-DC power converter signals the external switching device, which is upstream of the AC-DC power converter to turn on, thereby supplying the power to be converted to the AC-DC power converter.
In this invention the AC-DC power converter monitors the external upstream switching device either by qualifying that the power is, or is not, being supplied, or alternately, it may monitor the state of the external upstream switching device by an auxiliary means. Most often, and in our preferred embodiment, the external upstream switching device is an electrical contactor and the state of the device is monitored by detecting the presence of the AC power between phase inputs at the AC-DC power converter, by detecting the presence of AC voltage between at least one AC input terminal and earth ground, and/or by auxiliary contacts on the electrical contactor.
If the AC-DC power converter detects that the connected power is inappropriate, e.g., too high or too low in voltage, single phase as opposed to three phase, incorrect frequency, etc., it may elect to turn off the external upstream switching device to protect the AC-DC power converter and/or the downstream circuits (loads).
The AC-DC power converter can optionally elect to turn off the upstream external upstream switching device if the incoming power is of insufficient quality to support the requirements for the power to be delivered by the AC-DC power converter.
Another important element of the invention is to react when it has commanded the external upstream switching device to disconnect power and it detects that this has failed (or partially failed, i.e. disconnected only a portion of the incoming power circuits). When this occurs, it may do one or more of the following: sound an alarm, send a “safety breach” signal to other devices or, engage other means of rendering the output of the power converter safe, e.g., shorting the input or output of the power converter to blow upstream circuit protection devices, stopping the power conversion process, or, by using some supplemental power disconnect method internal to the Power Converter.
Upon receipt of a power-on command through the input command signal (24) the controller (10) will turn on the external switching device (3). Through an AC monitoring circuit (9), the controller (10) checks the quality of AC voltage supplied at the output of the switching device. If there are problems detected with the incoming AC supply the controller (10) turns off the external switching device.
The AC from the external switching device (3) is rectified into DC by a rectifier, preferably a bridge rectifier (4), but which could be any sort of AC-DC rectifier circuit known to the art, including a power factor corrected (PFC) rectifier circuit.
The DC output of the rectifier is coupled to a protective circuit which is controllable so that the output of the protective circuit can be controlled by an input to protect the DC supply to the load (13). In
The AC monitor (9), bridge rectifier (4), protective impedance (5) and protective impedance bypass (11) are rated to withstand voltages in excess of the rating of the AC-DC rectifier device (1). This allows the temporary connection to an AC source (2) which is in excess of the voltage ratings of the AC-DC rectifier device (1).
The protective impedance bypass (11) is only actuated when the controller (10) has determined it is safe to connect the output of the rectifier to the load. This can be done by detecting that the AC input voltage is appropriate (e.g. below the maximum rated voltage of the AC-DC rectifier device (1)) using the AC voltage monitor (9) and, optionally, by monitoring the charging of the filter capacitor (6) through the DC voltage monitor (12). By monitoring the time history of the capacitor's (6) voltage when being charged by the impedance (5) the controller (10) can calculate the asymptotic limit (final value) of the capacitor voltage before the charging is complete so it can take action before the voltage exceeds the limits of the load (13), capacitor (6) or the other sensitive circuits (7). This can be less expensive than measuring the AC input directly.
The provision of DC monitor (12) also allows the controller (10) to shut off the external switching device (3) when the output voltage exceeds a determined value, before damaging the circuits rated at lower voltages: the filter capacitor (6), the external load (13) and other sensitive circuits (7) that would be damaged by excessive voltage. It should be noted that this capability allows the invention to protect more than just the load (13) and the capacitor (6)—a typical embodiment might have other circuits or devices with voltage limits.
The controller may also monitor the DC output current in the load through the current sensor (8) If this function is employed, the controller (10) will disconnect the AC power source (2) with the external switching device (3) if the DC output current exceeds a determined value such as a maximum current rating of the AC-DC rectifier or the rating of the load (13), whichever is smaller.
If at any time the controller (10) attempts to turn-off the external switching device (3) and then detects that the external switching device has not disconnected all or some of the connections to the AC source (2), it may sound an alarm through annunciator (14). The controller (10) detects the failure of the external switching device to disconnect using the AC voltage monitor (9) or by monitoring the external-switching device through auxiliary sensing means (not shown).
The controller (10) may have a “power-OK” output (15) on which it asserts a signal when it determines that power quality is acceptable. This output may be coupled to a load so that the load device can react to problems in power quality. A safety switch (16) can be provided, which asserts a status signal (17) coupled to an input of the controller, by which an operator can indicate “Operate”, or, alternatively, “Stop” or “Faulted”.
The controller (10) may delay the turn-on of the external switching device (3) in order to limit the heating of internal components or components within the load from start-up currents in the system that could over stress components if the input command signal (24) is cycled too rapidly.
After receipt of a “power off” command on the power on/off input (24), the controller (10) may also first de-assert the power-OK signal (15) and delay turning off the external switching device (3) for a selected time, in order to allow the load time to react to de-assertion of the power-OK signal (15).
Instead of the protective impedance (5) and bypass (11) used in
The embodiment of
The embodiment of
The switching device (3) shown in
If at any time the controller (10) attempts to turn-off the external switching device (3) and then detects that the external switching device has not disconnected all or some of the connections to the AC source (2) by the AC voltage monitor (9), the additional contacts (25), or by monitoring the external-switching device through any other auxiliary sensing means known to the art, it may sound an alarm through annunciator (14) and/or stop the operation of the isolated converter stage (22).
The “PE” symbol shown in the diagram (25) is the international symbol for Protective Earth Ground, which can be used as a reference node by the AC voltage monitor (9) circuit to measure the presence of a Hazardous AC input even when only one phase is accidentally connected (e.g., from a contact failing to open on contactor (3)).
One example method that utilizes the apparatus elements to accomplish the functions outlined above is diagramed in the flowchart
Of the variables referenced in the flowchart, “time” is a continuously rolling count incremented on a precision periodic basis, e.g., every millisecond. “minoff” is a constant that is shortest allowable time between cycling the external upstream switching device off and then on again; “n” is a constant that is the time allowed to qualify the incoming power (in “time” units); “i” is the variable used to hold the time of the most recent turn-on of the external upstream switching device; “k” is the variable used to hold the time of the most recent turn-off of the external upstream switching device.
If it is OK, proceed to step 127
If it is not OK, then proceed to step 138
If it does exceed the limit, skip to step 137
If it does exceed the limit, skip to step 137
Check the time—is time-i>n?
If it is not, loop back to step 126
If it is less than the minimum, skip to step 135
If it is, skip to step 135
If the status is “Operate”, loop back to step 126
If the status is “Stop” or “Faulted”, continue to step 135
If it is not, Step 140 Sound an Alarm (14), otherwise proceed to step 141
It will be understood that this is given merely as an example of a method of operation appropriate for the invention, but that other variations and substitutions are possible within the teachings of the invention.
There are no commercial examples of AC-DC power converters (DC output power supplies, rectifiers, etc) that control both the on and off actuation of an external upstream switching devices, i.e., AC-DC power converters that control the supply power to them. Such a converter would control the on and off actuation of the external upstream switching device based upon control signaling to the AC-DC power converter. It would autonomously be able to shut off the external upstream switching device in exception circumstances and/or time the exact on or off switching of the external upstream switching device to enhance the operation of the system it is in.
In summary, then, the features of the invention which are believed to be novel are as follows:
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.
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|U.S. Classification||340/654, 361/18, 363/56.09, 323/205, 340/635, 340/664, 361/20, 363/80, 323/208, 340/657, 361/111, 361/23, 323/210|
|Cooperative Classification||H02H7/1252, H02H11/006|
|Nov 18, 2008||AS||Assignment|
Owner name: TEKNIC, INC., NEW YORK
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BUCELLA, THOMAS JOHN;DOMBROSKI, THOMAS P.;FUCHS, DAVID E.;AND OTHERS;REEL/FRAME:021852/0692
Effective date: 20081117
|May 31, 2011||CC||Certificate of correction|
|Jul 15, 2014||FPAY||Fee payment|
Year of fee payment: 4